Isolation and Characterization of an H 2 -Oxidizing Thermophilic Methanogen

Abstract

A thermophilic methanogen was isolated from enrichment cultures originally inoculated with sludge from an anaerobic kelp digester (55.degree. C). This isolate exhibited a temperature optimum of 55.degree.-60.degree. C and a maximum near 70.degree. C. Growth occurred throughout the pH range of 5.5-9.0, with optimal growth near pH 7.2. Although 4% salt was present in the isolation medium, salt was not required for optimal growth. The thermophile utilized formate or H2-CO2 but not acetate, methanol or methylamines for growth and methanogenesis. Growth in complex medium was very rapid and a minimum doubling time of 1.8 h was recorded in media supplemented with rumen fluid. Growth in defined media required the addition of acetate and an unknown factor(s) from digester supernatant, rumen fluid or Trypticase. Cells in liquid culture were oval to coccoid, 0.7-1.8 .mu.m in diameter, often occurring in pairs. The cells were easily lysed on exposure to O2 or 0.08 mg of sodium dodecyl sulfate/ml. The isolate was sensitive to tetracycline and chloramphenicol but not penicillin G or cycloserine. The DNA base composition was 59.69 mol% guanine plus cytosine.